Since you are using pslist i assume you're on win32. Then , instead of using a system call to get the process list you could use something like this code (there's a better thread about it somewhere but i can't seem to find it just now) .

It uses Win32::PerfLib to return a list of process and PIDs. This will save CPU time, only not enough to fight against a while (sleep 1) :|

ZlR.